In rotary machines such as steam turbines and the like, a seal assembly may be used to form a seal between two stationary components and/or between a stationary component and a rotating component so as to limit leakage therethrough. Such a seal assembly may have a number of arcuate sealing segments positioned adjacent to each other. The sealing segments generally may be disposed in an annular groove of one of the components. Each sealing segment further may have a sealing face in opposition to the other component. The sealing function may be achieved by creating relatively tight clearances between the sealing face of the sealing segments and the opposing components. Other types of sealing assembly configurations and components may be known.
During operation of the rotary machine, and more particularly during startup, shut down, and/or other transient operations, the components of the sealing assembly may experience different thermal expansion rates. These expansion rates may impact the spacing between the sealing segments as the components expand and contract and may lead to leakage therethrough. For example, inner-segment gap leakage may be the main source of leakage in many “zero leakage” seals that may be used about first nozzle locations and the like for many steam turbines. Inter-segment gap leakage has become a significant issue given the use of ever tighter radial clearances. Minimizing leakage between the sealing segment gaps thus may improve overall rotary machine performance and efficiency.
Segmented seals for use between a first component and a second component of a rotary machine usually are designed to have butt gaps between segments so that they will not go arch-bound and open up a radial clearance at the sealing face with leakage therethrough. In clearance seals, the butt gap leakage is relatively small, but it can become significant if the seal teeth clearance is reduced, such as in the “zero clearance” seal case where the seal teeth are in contact with their mating sealing surface because of the relatively slow motion therebetween. Because the leakage across the seal teeth became very small, the butt gap leakage becomes a main source of leakage.
There is thus a desire therefore for an improved sealing assembly that may limit inter-segment leakage therethrough as well as adequately accommodating differing thermal conditions. Such an improved sealing assembly also would improve overall machine performance and efficiency with the use of inexpensive and reliable components.